A desperate search is underway in Utah after two young brothers vanished alongside their father, with police warning the children could be in 'imminent danger' as fears grow over the mental state of the man accused of taking them.

Authorities issued an Amber Alert early on Sunday for one-year-old Will Richman and infant Wesley Richman after their father, Dane Stephen Richman, failed to show up for a scheduled custody exchange in Saratoga Springs on Saturday.

The children would spend alternate weeks with their parents but investigators say the boys have not been seen since before the missed exchange. 

It has now set off a desperate race against time as loved ones and law enforcement try to piece together clues as to their whereabouts.

Police have painted a deeply troubling picture of the missing father's recent behavior, saying there is growing concern for the children's safety because Richman, 46, was believed to be 'seriously depressed,' suffering financial problems, and had possibly abandoned his home before disappearing with the boys.

'There is concern for the safety and well-being of the children as the suspect has been seriously depressed, selling possessions, facing financial stress, and abandoned his home,' the Amber Alert states.

The warning has raised fears the children may face 'imminent danger of serious bodily harm or death,' according to investigators.

Will is described as about 2-foot-6 and 31 pounds with blonde or strawberry-colored hair and blue eyes, while Wesley is described as approximately 2-foot-2 and 23 pounds with blonde or strawberry-colored hair and blue eyes.

Their father, Dane, is described as 6-foot-2 and around 195 pounds with brown hair and green eyes.

The boys' aunt, Katie Walters, said the family knew that something was wrong after their mother, Lizzie Tomich, turned up at their deposition only to find her husband had fired his lawyer, telling him his services were no longer needed.

When Tomich found her husband wasn't picking up his phone she urged police to conduct a welfare check at his home.

Richman was last seen with the children after collecting them from his wife's home in Shelton, Washington, on May 16. 

He had told his wife that he was going to be away camping with the kids but when officers got to the house they found a moving truck pulling out of his driveway.

'He had completely moved out of his house that the children were supposed to be living in, and the moving truck was just actually pulling out of the driveway, and the police were able to stop the moving truck, and they asked what's going on,' Walters told ABC4. 

'They said they didn't even know because they never even saw the owner of the home while they were there. They only were communicating via text.'  

Walters said she found out that Richman had been giving away his possessions to neighbors including a new dresser for the baby's room that he had bought only weeks earlier.

'It was liquidating. On top of that, he had recently quit his job a week or so ago, so he no longer has a source of income. You put two and two together,' she said. 

'We have enough intel from the FBI and police to reasonably suspect that he has left the state of Utah.' 

Walters had a message for the boys' father directly: 'To Dane, just please be safe. We love you, and we love those kids. We just want you guys to come home safe. Please get somewhere safe: A hospital, a police department, fire department, anything. We just want you guys to be safe,' she said.

'He loves those boys so much. That's the only thing I could think of that led to this, I like to call it maybe an adult temper tantrum. You know, he loves those boys, and I've got to hold on to hope. There's no world without them.'

Police believe Richman and his two young sons may be traveling in a black 2025 Toyota Camry bearing Utah license plate A561HL, although investigators warned the vehicle could also be displaying a temporary tag that may make the plate difficult to identify.

Law enforcement agencies across Utah are now searching for the black Camry while urging drivers, business owners and residents to report any sightings immediately. 

'You'll be able to see them. Those little boys are so stinking cute. They have the brightest blonde hair and the biggest smiles you'll ever see. Oh my gosh. Wes, the baby, is the giggliest little baby,' aunt Walters described. 'Will and Wes are just adorable. I miss them so much.' 

It is a sentiment echoed by their mother who posted a heart-wrenching plea online. 

'I miss my babies !!! Please help me find them. They are my world!!!! I can't even describe how awful this is. Please please please help me find them!!!!', Tomich wrote. 

Police have not publicly disclosed where investigators believe Richman may be headed.